This application claims priority of German patent application no. 101 09 591.0, filed Feb. 28, 2001, the complete disclosure of which is hereby incorporated by reference.
The invention relates to a method of producing a hollow mixing rod and to a hollow mixing rod comprising four side parts, each of which is provided with one reflective inner side forming one side each of a hollow space, which extends from a light inlet area to a light outlet area and has a quadrangular cross-section.
In the case of such a hollow mixing rod, it is very important for its properties that the reflective inner sides of the four side parts be assembled such that no gap whatsoever is formed between them at which light losses would occur. In particular, if the quadrangular cross-section of the hollow space is neither rectangular nor square and, consequently, its cross-sectional sides converge in at least one corner at an angle which is not equal to 90xc2x0, the production of such a hollow mixing rod is very costly.
In view thereof, it is an object of the invention to provide a method of producing a hollow mixing rod, by which the hollow mixing rod is easily and accurately produced, even if two sides of the cross-section of the hollow space converge at an angle not equal to 90xc2x0. Further, a hollow mixing rod as mentioned above is to be improved such that it can be produced as easily as possible.
According to the invention, this object is achieved by the method of producing a hollow mixing rod having a hollow space of quadrangular cross-section, which method comprises the steps of producing a first and a second side part, each of which has a T-shaped cross-section comprising a crossbar and a central bar protruding therefrom, which comprises a reflective end surface averted from the crossbar and, viewed in cross-section, a first and a second side surface extending from the end surface to the crossbar, wherein, at least in the first side part, the end surface and the first side surface, viewed in cross-section, converge at an angle which is not equal to 90xc2x0, producing third and fourth side parts, each provided with a reflective, planar inner side, assembling the four side parts such that the end surfaces of the first and second side part face each other and the reflective inner sides of the third and fourth side parts, viewed in cross-section, extend parallel to each other and have their edge portions resting on the side surfaces of the central bars, so that the hollow space is limited by forming the quadrangular cross-section. This method requires the end surface of only one side part having a T-shaped cross-section to be chamfered relative to the side surfaces. Such chamfering of the end surface is possible in a particularly easy and accurate manner by grinding a T-shaped blank, whose end surface extends perpendicularly to the side surfaces. On the one hand, such grinding of the end surface may be performed with high accuracy and precision. On the other hand, said grinding may also be performed simultaneously on a plurality of side parts, so that a production in large quantities is also possible with the same high precision.
In order to achieve the desired planarity of the end surfaces, said end surfaces are preferably polished after grinding.
If the material of the T-shaped blank is a material which does not have sufficient reflective properties, the ground and optionally polished end surface may be additionally provided with a reflective coating. This may be realized, e.g., by reflective coating with a silver layer or by applying a dielectric reflective coating. Depending on the type of the reflective coating, a protective coating may additionally be applied on the reflective coating, if necessary.
The end surface may also be formed by milling, instead of by grinding, with the end surface preferably being polished as well.
The side parts may be manufactured from glass, metal, metal alloys, ceramics or plastics. If plastic material is used, the first and second side parts may be formed, e.g. by injection molding, together with the chamfered end surface. The end surface may preferably be subjected to further treatment, if the planarity of the end surface is to be improved. In this case, the end surface may also be provided with a reflective coating. If a metal or a metal alloy is used, the reflective property of the end surface can only be obtained by polishing. In the case of these materials, too, the side parts may already be formed with chamfered end surfaces, e.g. by casting methods. Alternatively, of course, grinding or milling is also possible for chamfering the end surface.
In a preferred embodiment of the production method according to the invention, once the four side parts have been assembled, a piece of shrink tubing is pulled over said four side parts, which is then heated. Due to said heating, the tubing shrinks or contracts and, consequently, urges the four side parts against each other. Since the shrink tubing retains its contracted shape upon cooling, the side parts become permanently fixed. The shrink tubing may be disposed in the central region of the hollow mixing rod, as viewed in the longitudinal direction thereof. Alternatively, two pieces of shrink tubing may be provided at the respective end sections of the hollow mixing rod, as viewed in the longitudinal direction thereof. The use of the shrink tubing leads to a simple and effective manner of fixing the four side parts relative to each other, which is easily carried out without any problem. In particular, as the four side parts are urged together by the shrink tubing, this has the effect that no gaps are present between the reflectively coated or reflective inner sides, so that the hollow mixing rod is easy to produce with the required high accuracy.
The hollow mixing rod according to the invention comprising four side parts, each of which has a planar, reflective inner side forming one side each of a hollow space having a quadrangular cross-section and extending from a light inlet area to a light outlet area, is wherein the first and second side parts each have a T-shaped cross-section comprising a crossbar and a central bar which protrudes therefrom and whose end surface averted from the crossbar forms the reflective inner side of the side part and which comprises, viewed in cross-section, a first and a second side surface extending from the end surface to the crossbar, with the reflective inner sides of the third and fourth side parts being disposed parallel to each other, when viewed in cross-section, and having their edge portions resting on the side surfaces of the central bars, whereby, at least in the first side part, the end surface and the first side surface, viewed in cross-section, converge at an angle which is not equal to 90xc2x0. Thus, the hollow mixing rod according to the invention is particularly easy to produce, since forming a cross-section of the hollow space wherein two sides converge in one corner at an angle which is not equal to 90xc2x0 merely requires, e.g., that the end surface of the first side part be obliquely ground. This is easily and simply possible with the required high accuracy. Thus, the first side part preferably comprises an obliquely ground end surface. Consequently, the end surface of the central bar defines the angle at which the two sides of the cross-section converge and which is not equal to 90xc2x0. Further, the edge portions of the inner sides of the third and fourth side part rest on the side surfaces of the central bars, so that the central bars of the first and second side part also serve to predetermine and to maintain the distance between the reflective inner sides of the third and fourth side parts.
In a further advantageous embodiment of the hollow mixing rod according to the invention, the four side parts are held together by a piece of shrink tubing. The use of shrink tubing for holding together and fixing the four side parts results in a simplified manufacture of the hollow mixing rod, since the shrink tubing only needs to be fitted over the four side parts and then heated. The fixing and positioning of the four side parts is then effected virtually automatically, because the contracting shrink tubing adapts to the external shape of the four side parts and presses them against each other. By being urged against each other in this manner, the third and and fourth side part are guided with their reflective inner sides on the side surfaces of the central bars and then urged against the crossbars with their longitudinal sides. The shrink tubing also prevents the hollow mixing rod having gaps between the reflective inner sides, so that the reflective surfaces lie next to each other in a manner impermeable to light.
Advantageously, in the hollow mixing rod according to the invention, the end surface and the first side surface of the second side part, viewed in cross-section, may also converge at an angle not equal to 90xc2x0. This allows a symmetrical cross-sectional shape of the hollow space, e.g. a trapezoidal cross-section, to be realized. However, it is possible also to realize parallelogram-shaped cross-sections, or even cross-sections whose cross-sectional sides converge at different angles in each of the four corners thereof.
In particular, the third and fourth side parts of the hollow mixing rod according to the invention may each have an I-shaped cross-section, with the longitudinal sides of the third and fourth side parts contacting the crossbars of the first and second side parts. Thus, a very compact hollow mixing rod is realized with a stable structure.
The hollow mixing rod according to the invention may be used, in particular, in an optical device for generating and projecting an image. The optical device preferably contains a light source, an imaging element and projection optics, the hollow mixing rod being interposed between the light source and the imaging element. The light from the light source is coupled into the hollow mixing rod via the light inlet area and guided inside the hollow mixing rod to the light outlet area. The light rays impinging on the reflective inner sides are guided to the light outlet area by one or more reflexions. This has the effect that the luminance distribution in the light outlet area is more uniform as compared with that in the light inlet area, so that a field which is illuminating as uniformly as possible is generated in the light outlet area. This illuminating field is imaged, e.g. by interposed intermediate optics, on the imaging element so as to illuminate the latter as uniformly as possible. The imaging element is controlled by a control unit on the basis of predetermined image data, in order to generate the image which is projected onto a projection surface by the projection optics.
The invention will be explained in more detail below, byway of example and with reference to the drawings.